TETRANDRINE AS A CALCIUM ANTAGONIST
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1. The Ca(2+)-antagonism of tetrandrine (TET) on the Ca2+ mobilization in various types of cells were reviewed. Inositol trisphosphate (IP3)-generating drugs were used as Ca(2+)-mobilizing agonists and the effects were compared with those produced by using the microsomal Ca(2+)-ATPase inhibitor thapsigargin (TG), which is a tool for analysing Ca2+ store-regulated Ca2+ entry (capacitative Ca2+ entry). 2. In rat phaeochromocytoma PC12 cells, 100 mumol/L TET abolished high K+ (30 mmol/L)-induced sustained increases in cytoplasmic Ca2+ concentrations ([Ca2+]i) and partially inhibited bradykinin (1 mumol/L)- or TG (100 nmol/L)-induced Ca2+ entry. 3. In NIH/3T3 fibroblasts and rat parotid acinar cells, 100 mumol/L TET abolished Ca2+ entry induced by bombesin (1 mumol/L) and carbachol (100 mumol/L), respectively, or TG (100 nmol/L). However, in the human leukaemia T cell line Jurkat, 100 mumol/L TET did not inhibit Ca2+ entry evoked by either the anti-CD3 antibody OKT3 (10 mg/L) or TG (100 nmol/L). 4. In rat glioma C6 cells, the effects of TET on Ca2+ mobilization were further examined. At a high concentration, TET (300 mumol/L) alone did not affect [Ca2+]i in C6 cells. Tetrandrine inhibited the peak and sustained increases in [Ca2+]i induced by bombesin and TG in a dose-dependent manner. Although TET or TG did not produce increases in IP3, TET did inhibit increases in IP3 produced by bombesin. 5. Our results suggest that the action of TET on Ca2+ entry is dependent on cell types and that TET inhibits both Ca2+ entry from the extracellular medium and Ca2+ release from intracellular stores in rat glioma C6 cells.
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